Lithographic apparatus, device manufacturing method and device manufacturing thereby

ABSTRACT

A lithographic projection apparatus includes conduits which supply utilities to components in a vacuum chamber such as object tables and/or associated motors and/or sensors. The conduits are shielded from exposure to the vacuum by conduit conducts having at least the same number of degrees of freedom as their associated object table.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This is a continuation application of U.S. application Ser. No.09/989,700, filed Nov. 21, 2001, which in turn claims priority fromEuropean Patent Application No. 00310637.4, filed Nov. 30, 2000, both ofwhich are herein incorporated by reference in their entireties.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to lithographic projectionapparatus, and more particularly to apparatus including conduits forproviding utilities such as power, water, control signals and gasesthrough cables, hoses or pipes to a movable component in a vacuumchamber.

[0004] 2. Background of the Related Art

[0005] A lithographic projection apparatus in accordance with thepresent invention generally includes a radiation system for providing aprojection beam of radiation, a first object table for supportingpatterning structure, the patterning structure serving to pattern theprojection beam according to a desired pattern, a second object tablefor holding a substrate, a vacuum chamber provided with a first gasevacuating means for generating a vacuum beam path for the projectionbeam, a projection system for projecting the patterned beam onto atarget portion of the substrate and conduits for providing utilities toa component moveable in at least one degree of freedom in said vacuumchamber.

[0006] The term “patterning structure” as here employed should bebroadly interpreted as referring to means that can be used to endow anincoming radiation beam with a patterned cross-section, corresponding toa pattern that is to be created in a target portion of the substrate;the term “light valve” can also be used in this context. Generally, thesaid pattern will correspond to a particular functional layer in adevice being created in the target portion, such as an integratedcircuit or other device (see below). Examples of such patterningstructure include:

[0007] A mask. The concept of a mask is well known in lithography, andit includes mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. Placementof such a mask in the radiation beam causes selective transmission (inthe case of a transmissive mask) or reflection (in the case of areflective mask) of the radiation impinging on the mask, according tothe pattern on the mask. In the case of a mask, the first object tablewill generally be a mask table, which ensures that the mask can be heldat a desired position in the incoming radiation beam, and that it can bemoved relative to the beam if so desired.

[0008] A programmable mirror array. An example of such a device is amatrix-addressable surface having a viscoelastic control layer and areflective surface. The basic principle behind such an apparatus is that(for example) addressed areas of the reflective surface reflect incidentlight as diffracted light, whereas unaddressed areas reflect incidentlight as undiffracted light. Using an appropriate filter, the saidundiffracted light can be filtered out of the reflected beam, leavingonly the diffracted light behind; in this manner, the beam becomespatterned according to the addressing pattern of the matrix-adressablesurface. The required matrix addressing can be performed using suitableelectronic means. More information on such mirror arrays can be gleaned,for example, from United States patents U.S. Pat. No. 5,296,891 and U.S.Pat. No. 5,523,193, which are incorporated herein by reference. In thecase of a programmable mirror array, the first object table may beembodied as a frame or table, for example, which may be fixed or movableas required.

[0009] A programmable LCD array. An example of such a construction isgiven in United States patent U.S. Pat. No. 5,229,872, which isincorporated herein by reference. As above, the first object table inthis case may be embodied as a frame or table, for example, which may befixed or movable as required.

[0010] For purposes of simplicity, the rest of this text may, at certainlocations, specifically direct itself to examples involving a mask andmask table; however, the general principles discussed in such instancesshould be seen in the broader context of the patterning structure ashereabove set forth.

[0011] Lithographic projection apparatus can be used, for example, inthe manufacture of integrated circuits (ICs). In such a case, thepatterning structure may generate a circuit pattern corresponding to anindividual layer of the IC, and this pattern can be imaged onto a targetportion (e.g. comprising one or more dies) on a substrate (siliconwafer) that has been coated with a layer of radiation-sensitive material(resist). In general, a single wafer will contain a whole network ofadjacent target portions that are successively irradiated via theprojection system, one at a time. In current apparatus, employingpatterning by a mask on a mask table, a distinction can be made betweentwo different types of machine. In one type of lithographic projectionapparatus, each target portion is irradiated by exposing the entire maskpattern onto the target portion at once; such an apparatus is commonlyreferred to as a wafer stepper. In an alternative apparatus—commonlyreferred to as a step-and-scan apparatus—each target portion isirradiated by progressively scanning the mask pattern under theprojection beam in a given reference direction (the “scanning”direction) while synchronously scanning the substrate table parallel oranti-parallel to this direction; since, in general, the projectionsystem will have a magnification factor M (generally <1), the speed V atwhich the substrate table is scanned will be a factor M times that atwhich the mask table is scanned. More information with regard tolithographic devices as here described can be gleaned, for example, fromU.S. Pat. No. 6,046,792, incorporated herein by reference.

[0012] In a manufacturing process using a lithographic projectionapparatus, a pattern (e.g. in a mask) is imaged onto a substrate that isat least partially covered by a layer of radiation-sensitive material(resist). Prior to this imaging step, the substrate may undergo variousprocedures, such as priming, resist coating and a soft bake. Afterexposure, the substrate may be subjected to other procedures, such as apost-exposure bake (PEB), development, a hard bake andmeasurement/inspection of the imaged features. This array of proceduresis used as a basis to pattern an individual layer of a device, e.g. anIC. Such a patterned layer may then undergo various processes such asetching, ion-implantation (doping), metallization, oxidation,chemo-mechanical polishing, etc., all intended to finish off anindividual layer. If several layers are required, then the wholeprocedure, or a variant thereof, will have to be repeated for each newlayer. Eventually, an array of devices will be present on the substrate(wafer). These devices are then separated from one another by atechnique such as dicing or sawing, whence the individual devices can bemounted on a carrier, connected to pins, etc. Further informationregarding such processes can be obtained, for example, from the book“Microchip Fabrication: A Practical Guide to Semiconductor Processing”,Third Edition, by Peter van Zant, McGraw Hill Publishing Co., 1997, ISBN0-07-067250-4, incorporated herein by reference.

[0013] For the sake of simplicity, the projection system may hereinafterbe referred to as the “lens”; however, this term should be broadlyinterpreted as encompassing various types of projection system,including refractive optics, reflective optics, and catadioptricsystems, for example. The radiation system may also include componentsoperating according to any of these design types for directing, shapingor controlling the projection beam of radiation, and such components mayalso be referred to below, collectively or singularly, as a “lens”.Further, the lithographic apparatus may be of a type having two or moresubstrate tables (and/or two or more mask tables). In such “multiplestage” devices the additional tables may be used in parallel, orpreparatory steps may be carried out on one or more tables while one ormore other tables are being used for exposures. Twin stage lithographicapparatus are described, for example, in U.S. Pat. No. 5,969,441 and WO98/40791, incorporated herein by reference.

[0014] In a lithographic apparatus, the size of features that can beimaged onto the substrate is limited by the wavelength of the projectionradiation. To produce integrated circuits with a higher density ofdevices and hence higher operating speeds, it is desirable to be able toimage smaller features. While most current lithographic projectionapparatus employ ultraviolet light generated by mercury lamps or excimerlasers, it has been proposed to use shorter wavelength radiation ofaround 13 nm. Such radiation is termed extreme ultraviolet (EUV) or softx-ray, and possible sources include laser produced plasma sources,discharge plasma sources or synchrotron radiation from electron storagerings. An outline design of a lithographic projection apparatus usingsynchrotron radiation is described in “Synchrotron radiation sources andcondensers for projection x-ray lithography”, J B Murphy et al, AppliedOptics Vol. 32 No. 24 pp 6920-6929 (1993).

[0015] Other proposed radiation types include electron beams and ionbeams. Further information with regard to the use of electron beams inlithography can be gleaned, for example, from U.S. Pat. No. 5,079,122and U.S. Pat. No. 5,260,151, as well as from EP-A-0 965 888. These typesof beam share with EUV the requirement that the beam path, including themask, substrate and optical components, be kept in a high vacuum. Thisis to prevent absorption and/or scattering of the beam, whereby a totalpressure of less than about 10⁻⁶ millibar is typically necessary forsuch charged particle beams. Otherwise, for apparatus using EUVradiation, the total vacuum pressure need only be between 10⁻³ and 10⁻⁵millibar. Optical elements for EUV radiation can be spoiled, by thedeposition of carbon layers on their surface, which imposes theadditional requirement that hydrocarbon partial pressures shouldgenerally be kept as low as possible, for example below 10⁻⁸ or 10⁻⁹millibar.

[0016] Working in a high vacuum imposes quite onerous conditions on thecomponents that must be put into the vacuum. For components inside thevacuum chamber, materials that minimize or eliminate contaminant andtotal outgassing, i.e. both outgassing from the materials themselves andfrom gases adsorbed on their surfaces, should be used. It has been foundthat for the desired degree of movement required by the object holders,conduits can be made of plastics materials such that they are flexibleenough. These types of materials often are deleterious to the vacuum inthe vacuum chamber because outgassing of contaminants as described abovewill occur. There are plastics better suited for vacuum applications(for example teflon) but the large number of cables and lines which arerequired to be lead through the vacuum present a large surface area tooutgassing of contaminants. It will be difficult to get a partiallyhydrocarbon pressure below 10⁻⁸ or 10⁻⁹ millibar, for example, whenplastic conduits are used. Furthermore, the risk of leaks from conduitsmakes their use impractical. It would be very desirable to be able toreduce the use of conduits. However, conventional designs of substrate,mask and transfer stages are very complicated and employ large numbersof sensors and drive arrangements, which all need a large numbers ofconduits for conveying water and gases and for protecting electricwiring.

[0017] To circumvent this problem it has been proposed in U.S. Pat. No.4,993,696 to use metal pipes made of stainless material for the supplyand exhaustion of an operating fluid or gas in a vacuum ambience. Twoadjacent pipes may then be coupled with each other by a joint, which isarranged to allow swingable movement of one of the pipes relative to theother. The metal pipes will not suffer from outgassing as the nylonconduits will do. A disadvantage of the joints is that it is verydifficult to design joints that are totally closed for fluids or gasesin a vacuum environment. Therefore, there may be leakage of gasesthrough the joint to the vacuum environment that will contaminate thevacuum environment.

[0018] Another solution has been proposed by European Patent Application1052549. In this publication conduits are fed through hollow pipes thatare rigidly connected to a movable object table and which pipes are usedto transfer movements from outside a vacuum chamber to said table. Thepipes are hollow and the pressure within the pipes is equal to thepressure outside the vacuum chamber. Between the wall of the vacuumchamber and the pipes differentially pumped seals are used to preventthe leakage of air to the vacuum chamber and at the same time allowingfor movement of the object table.

SUMMARY OF THE INVENTION

[0019] One aspect of the present invention provides a lithographicapparatus with substantially reduced problems due to out-gassing ofmaterials in the vacuum chamber.

[0020] According to the present invention there is provided alithographic projection apparatus comprising:

[0021] a radiation system for providing a projection beam of radiation;

[0022] a first object table for supporting patterning structure, thepatterning structure serving to pattern the projection beam according toa desired pattern;

[0023] a second object table for holding a substrate;

[0024] a vacuum chamber provided with a first gas evacuating means forgenerating a vacuum beam path for the projection beam;

[0025] a projection system for projecting the patterned beam onto atarget portion of the substrate; and

[0026] conduits for providing utilities to a component moveable in atleast one degree of freedom in said vacuum chamber, characterized inthat the apparatus further comprises:

[0027] a conduit shield for shielding the vacuum of said vacuum chamberfrom a space comprising the conduits, said conduct shield beingconstructed and arranged to allow for movement of the component in saidat least one degree of freedom, and

[0028] a second gas evacuating means for providing a vacuum in the spacecomprising the conduits.

[0029] The term utilities as here employed refers to the water, gas,electricity and signals that must be provided to the moveable component.The term conduit refers to the cables and tubes that are used totransport the utilities to the moveable component. More specifically theterm conduits refers to such items as power cords, signal carriers, gastubes (e.g. for supplying gas to a gas bearing in the table), coolanttubes, etc. Moveable components inside the vacuum chamber including themask table and/or the substrate table and/or associated motors and/orsensors may be connected to a frame outside the vacuum chamber in thismanner (using a distinct conduit conduct for each component).

[0030] It will be difficult to make the conduit shield airtight and atthe same time flexible enough to allow for movement of the component.The inventors have solved this problem by the use of a conduit shieldthat will shield the vacuum chamber from the space comprising theconduits but need not to be completely airtight. The leakage through thenot completely airtight conduit shield will be minimized by having asmall or even no pressure difference between the vacuum in the vacuumchamber and the space comprising the conduits. The conduits will be in aspace that is made vacuum by a second gas evacuating means and that willbecome dirty due to outgassing of the conduits. The dirty vacuum in thespace comprising the conduits will not negatively effect the vacuum inthe vacuum chamber because the use of the almost airtight conduit shieldand the little pressure difference that exists between the spacecomprising the conduits and the vacuum chamber. The outflow ofcontaminants through the not completely airtight conduit shield to thevacuum chamber will thereby be minimized. At the same time the loosenedrequirements for the airtightness of the conduit shield will make itmore easy to construct a conduit shield that allows for movement of themovable component. An other advantage of the construction according tothe invention is that the force exerted on the conduit shield by any gaspressure in the space comprising the conduits is decreased by the secondgas evacuating means so that lighter building materials can be used.

[0031] The vacuum in the vacuum chamber may have a hydrocarbon partialpressures below 10⁻⁸ or 10⁻⁹ millibar, for example, while that partialpressure in the space comprising the conduits will be substantialhigher. The vacuum provided to the space comprising the conduits may bearound 10⁻³ millibar and the vacuum provided to the vacuum chamber maybe around 10⁻⁵ millibar or lower in the presence of the opticalcomponents.

[0032] According to a second aspect of the present invention there isprovided a device manufacturing method comprising the steps of:

[0033] providing a substrate that is at least partially covered by alayer of radiation-sensitive material;

[0034] providing a vacuum to a first vacuum chamber;

[0035] providing utilities through conduits to at least one componentmoveable in at least a first direction in said first vacuum chamber;

[0036] projecting a projection beam of radiation using a radiationsystem through said vacuum chamber;

[0037] using patterning structure to endow the projection beam with apattern in its cross-section;

[0038] projecting the patterned projection beam of radiation onto atarget portion of the layer of radiation-sensitive material,

[0039] characterized in that the method comprises the steps of:

[0040] shielding said vacuum in said vacuum chamber with a conduitshield from said conduits,

[0041] moving said conduit shield so as to follow the moveablecomponent; and

[0042] providing a second vacuum in a space comprising the conduits andseparated by the conduit shield from said vacuum chamber.

[0043] Although specific reference may be made in this text to the useof the apparatus according to the invention in the manufacture of ICs,it should be explicitly understood that such an apparatus has many otherpossible applications. For example, it may be employed in themanufacture of integrated optical systems, guidance and detectionpatterns for magnetic domain memories, liquid-crystal display panels,thin-film magnetic heads, etc. The skilled artisan will appreciate that,in the context of such alternative applications, any use of the terms“reticle”, “wafer” or “die” in this text should be considered as beingreplaced by the more general terms “mask”, “substrate” and “targetportion”, respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The present invention and its attendant advantages will bedescribed below with reference to exemplary embodiments and theaccompanying schematic drawings, in which:

[0045]FIG. 1 depicts a lithographic projection apparatus according to afirst embodiment of the invention;

[0046]FIG. 2 is a schematic plan view showing a conduit conductaccording to the first embodiment;

[0047]FIG. 3 is a schematic showing the position of first and secondconduit conducts according to the first embodiment in normal operation;

[0048]FIG. 4 is a schematic showing the positions of first and secondconduit conducts according to the first embodiment during initial swapmovements;

[0049]FIG. 5 is a schematic showing the positions of first and secondconduit conducts according to the first embodiment during swap;

[0050]FIG. 6 is a schematic showing the positions of the first andsecond conduit conducts according to the first embodiment during normaloperation;

[0051]FIG. 7 is a schematic showing a conduit conduct of the secondembodiment;

[0052]FIG. 8 is a schematic showing a conduit conduct of the thirdembodiment;

[0053]FIG. 9 is a schematic showing a conduit conduct of the fourthembodiment;

[0054]FIG. 10a is a schematic sectional view showing a joint of thefifth embodiment;

[0055]FIG. 10b is a variation on the joint of the fifth embodiment;

[0056]FIG. 11 is a schematic showing an inner member of a joint of asixth embodiment;

[0057]FIG. 12 is a schematic plan view showing the joint of the sixthembodiment;

[0058]FIG. 13 is a cross-sectional view of a differential gas bearingaccording to a seventh embodiment of the invention;

[0059]FIG. 14 is a cross-sectional view of the substrate table andforearm of the positioning means of an eighth embodiment of thelithographic projection apparatus according to the invention;

[0060]FIG. 15 is a cross-sectional view of the substrate table andforearm of the positioning means of a ninth embodiment of thelithographic projection apparatus according to the invention; and

[0061]FIG. 16 is a cross-sectional view of the substrate table andforearm of the positioning means of a tenth embodiment of thelithographic projection apparatus according to the invention.

[0062] In the various drawings, like parts are indicated by likereferences.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0063] Embodiment 1

[0064]FIG. 1 schematically depicts a lithographic projection apparatus 1according to the invention. The apparatus comprises:

[0065] a radiation system LA, IL for supplying a projection beam PB ofradiation (e.g. UV or EUV radiation, electrons or ions);

[0066] a first object table (mask table) MT provided with a first object(mask) holder for holding a mask MA (e.g. a reticle), and connected tofirst positioning means PM for accurately positioning the mask withrespect to item PL;

[0067] a second object table (substrate table) W2T provided with asecond object (substrate) holder for holding a substrate W2 (e.g. aresist-coated silicon wafer), and connected to second positioning meansP2W for accurately positioning the substrate with respect to item PL;

[0068] a third object table (substrate table) W3T provided with a thirdobject (substrate) holder for holding a substrate W3 (e.g. aresist-coated silicon wafer), and connected to third positioning meansP3W for accurately positioning the substrate with respect to item PL;and

[0069] a projection system (“lens”) PL (e.g. a refractive orcatadioptric system, a mirror group or an array of field deflectors) forimaging an irradiated portion of the mask MA onto a target portion C ofthe substrate W2, W3.

[0070] The radiation system comprises a source LA which produces a beamof radiation (e.g. an undulator or wiggler provided around the path ofan electron beam in a storage ring or synchrotron, a plasma source, anelectron or ion beam source, a mercury lamp or a laser). This beam iscaused to traverse various optical components included in illuminationsystem IL so that the resultant beam PB has a desired shape andintensity distribution in its cross-section.

[0071] The beam PB subsequently impinges upon the mask MA which is heldin a mask holder on a mask table MT. Having been selectively reflected(or transmitted) by the mask MA, the beam PB passes through the “lens”PL, which focuses the beam PB onto a target portion C of the substrateW2, W3. With the aid of the positioning means P2W, P3W andinterferometric displacement measuring means IF, the substrate tableW2T, W3T can be moved accurately, e.g. so as to position differenttarget portions C in the path of the beam PB. Similarly, the positioningmeans PM and interferometric displacement measuring means IF can be usedto accurately position the mask MA with respect to the path of the beamPB, e.g. after mechanical retrieval of the mask MA from a mask libraryor during a scanning motion. In the prior art, movement of the objecttables MT, W2T is generally realized with the aid of a long-strokemodule (course positioning) and a short-stroke module (finepositioning), which are not explicitly depicted in FIG. 1.

[0072] The depicted apparatus can be used in two different modes:

[0073] In step mode, the mask table MT is kept essentially stationary,and an entire mask image is projected at once (i.e. a single “flash”)onto a target portion C. The substrate table W2T, is then shifted in theX and/or Y directions so that a different target portion C can beirradiated by the beam PB;

[0074] In scan mode, essentially the same scenario applies, except thata given target portion C is not exposed in a single “flash”. Instead,the mask table MT is movable in a given direction (the so-called “scandirection”, e.g. the Y direction) with a speed v, so that the projectionbeam PB is caused to scan over a mask image; concurrently, the substratetable W2T, is simultaneously moved in the same or opposite direction ata speed V=Mv, in which M is the magnification of the lens PL (e.g., M=¼or ⅕). In this manner, a relatively large target portion C can beexposed, without having to compromise on resolution.

[0075] In a lithographic projection apparatus according to the presentinvention, at least one of first and second object tables are providedin a vacuum chamber 20. The vacuum inside the vacuum chamber 20 iscreated with the vacuum evacuating means VE, for example a pump.

[0076] Much equipment is associated with an object table, such asalignment sensors, air bearings with differential vacuum seals,positioning motors and actuators which require utilities such as power,control signals, vacuum and gasses and supply utilities such asmeasurement signals and further control signals. These utilities aresupplied by conduits such as, for example, hoses, pipes, electricalcables etc. Although the conduit shield of the present invention isdescribed in relation to an embodiment with two object tables, it isequally applicable to a lithographic projection apparatus with only asingle object table or to other moveable components in the vacuumchamber.

[0077] Contamination control is a major issue. A small number ofhydrocarbon (C_(x)H_(y)) mono-layers on the mirrors, for instance, willlead to an unallowable reduction in the reflection efficiency of thesemirrors. In a “clean” vacuum environment, materials like plastics andelastomers continuously outgas and hollow sections of constructions likescrew joints tend to increase gas load (mainly water and hydrocarbons)and contamination via virtual leakage.

[0078] By shielding the conduits providing utilities to the objecttables using conduit shields, which each have at least the same numberof degrees of freedom as their associated object tables, it is possiblefor the conduits to be in a dirty vacuum along substantially their wholelength. This helps to meet the vacuum requirements by reducing theamount of hydrocarbons exposed in the vacuum chamber 20 and also helpsreducing the risks in case of the rupture of a coolant line. The numberof joints (both rotational and translational) and arm portions can bevaried depending on the required number of degrees of freedom ofmovement of the respective moveable component. For example the conduitshield in the form of a conduit conduct may only be required to have onearm which is not necessarily rotatable about a joint.

[0079]FIG. 2 shows only one conduit conduct 100 connecting conduits 24from outside of the vacuum chamber 20 to the object table W2T. The firstembodiment of the present invention has two such object tables. Theconduits 24 pass through a side wall 21 of the vacuum chamber 20 at aninput 12 to the conduit conduct 100 which comprises three hollow andelongate arm portions 107, 110, 120. Translation arm portion 107 istranslatable relative to the vacuum chamber side wall 21. This isaccomplished by arranging the outer surface of translating arm portion107 to be in sliding contact with the inside surface of a receivingtranslation arm portion 109. A vacuum seal 108 may be provided tominimize the outflow of gases from the space comprising the conduits 24to the vacuum chamber 20.

[0080] First arm portion 110 is joined at one end to translating armportion 107 via second joint 105 and is rotatable about second joint105. At the other end, first arm portion 110 is rotatably joined to anend of second arm portion 120 via first joint 115. The object table W2Tis joined to second arm portion 120 at the other end. The joints 105,115 and arm portions 107, 110, 120 are substantially airtight andtherefore in this way the conduits 24 are provided to the object tableW2T without being exposed to the vacuum in the vacuum chamber 20 and, ifrequired, may be provided under manufacturer chosen conditions. Iftranslation joints are used, it may be useful to provide a rough vacuumin the conduit conduct 100 such that the forces necessary to activatethe joint are not excessively large (if the conduit is under atmosphericpressure, the vacuum in the vacuum chamber generates a force which actsto extend the translation joint). A rough vacuum is also useful incertain circumstances because the air tightness requirements for thejoints are in that case loosened and deformation of the conduit conduct100 is less likely to occur. This deformation may be detrimental to theworking of the vacuum seals. To create the rough vacuum a second vacuumevacuating means VE2 may be provided to pump the air out of the conduitconduct 100.

[0081] The conduit conducts 100 may comprise torque motors in the joints105, 115 such that the conduit conduct 100 can position the object tableW2T. It is also possible that the conduit conduct 100 moves under theinfluence of the positioning means of the object table W2T. That is theconduit conducts 100 can be passive in that it does not comprise anydriving motors and only moves under the influence of the object tableW2T. If the conduit conduct is passive it might be advantageously tomake a prediction of the force exerted by the conduit conduct 100 on theobject table W2T so that feed forward can be compensated by thepositioning means for the influence of the mass of the conduit conduct100 on the movements of the object table W2T. This can be done either bycalibration of the force influence or by making an algorithm calculatingthis force influence. Alternatively, force sensors can be used betweenthe object table W2T and the conduit conduct that measure the forceexerted by the object table W2T on the conduit conduct 100 and feed backcompensate that force by adjusting the force exerted by the positioningmeans. Further information with regard to such a feed back system can begleaned from European Patent Application EP 1 018 669 incorporatedherein by reference. In some embodiments the conduit conducts 100themselves can be used to position the object table W2T. It is possibleto provide sensors in the joints for measuring the position of theobject table W2T. The measurement thus obtained can be used forcommutation purpose of the positioning means of the object table W2T.The positioning means may be a planar motor as described in WO 01/18944incorporated herein by reference.

[0082] Alternatively, a differential vacuum seal at 108 a and air, orgas, bearing at 108 b can be provided between surface 107, 109 to allowfor low friction movement between the arm portions 107, 109 while stillmaintaining the vacuum in the vacuum chamber 20. A differential vacuumseal and air, or gas, bearing assembly 108 a, 108 b is described indetail in the seventh embodiment.

[0083] It is advantageous in a lithographic apparatus to have two objecttables for holding substrates which can be driven independently. In thisway it is possible to be measuring or performing some other functionsuch as unloading a previously exposed wafer and loading a new wafer ina measuring area at the same time as exposing a different, previouslyunexposed wafer, in the exposure area. The exchange of wafer tablesbetween the measuring and exposure areas is called “swap”. In the firstembodiment, a third object table, designated W3T in FIG. 1 as well as asecond object table W2T is provided for this purpose.

[0084] It is advantageous to reduce the size of the apparatus. The firstembodiment achieves this through the arrangement of the first and secondconduit conducts associated with their respective second and thirdobject tables. Furthermore, the arrangement reduces the amount ofrotation of the first and second joints required to move the substratetable in the exposure and measuring areas and to transfer the substratetable from the exposure area to the measuring area or visa versa. Thisreduces stresses on the conduits and subsequently increases apparatuslifetime.

[0085] In the lithography apparatus of the first embodiment of thepresent invention, while one of the second or third object tables is inan exposure area in which the wafer held by the respective object tableis irradiated, the other one of the second and third object tables is ina measuring area where the wafer is measured, loaded and offloaded.

[0086]FIG. 3 shows in plan the second object table W2T and the thirdobject table W3T positioned in the measuring area 300 and exposure area200, respectively. First conduit conduct 100 provides utilities tosecond object table W2T and second conduit conduct 150 providesutilities to the third object table W3T.

[0087] First and second conduit conducts 100, 150 are identical andcomprise a first arm portion 110, 160 and a second arm portion 120, 170which are rotatably connected at first joint 115, 165. The first armportions of the first and second conduit conducts 100, 150 are rotatablerelative to the exposure area 200 (first working zone), the measuringarea 300 (second working zone) and the lithographic apparatus aroundsecond joints 105, 155. As shown in FIG. 3 when the second object tableis in the measuring position, the second joint 105 of the first conduitconduct 100 rotates around a second position 102. In the second positionthe second object table is positionable within the measuring area 300.In contrast, when the third object table W3T is positioned within theexposure area 200, the second joint 155 of the second conduit conduct150 is in a first position 151. The second position 102 of the firstconduit conduct 100 is generally equidistant from the exposure area 200and the measuring area 300 and the first position 151 of the secondconduit conduct 150 is generally equidistant from the exposure area 200and measuring area 300. The second joints 105, 155 are translatable fromthe first to second positions 101,102,151,152 and visa versa throughtranslation joints which comprise translating arm portions 107,157attached to second joints 105, 155 which slide in receiving arm portions109, 159 to move the first joints from the first to second positions101, 102, 151, 152. The sliding seal is maintained by differentialvacuum seals 108 a, 158 a and air bearings 108 b, 158 b.

[0088] A “swap” operation, in which the second object table W2T movesfrom one of the exposure 200 and measuring 300 areas to the other areaand the third object table W3T moves in the opposite direction, isdepicted schematically in FIGS. 4 and 5. Although FIGS. 4 and 5illustrate one combination of movements which result in so-called“swap”, the sequence of movements could be in a different order.

[0089] As is shown in FIG. 4, if swap is to be initiated, the first stepis the translation of the second joint 105, 155 of both first and secondconduit conducts. In the case of the second object table W2T, the secondjoint 105 of the first conduit conduct 100 moves from its secondposition 102 to a first position 101 which is positioned closer to theexposure area 200 than to the measuring area 300. During this operation,the second object table W2T remains substantially within the measuringarea 300 and it may move within that area. In the case of the thirdobject table W3T, the second joint 155 of the second conduit conduct 150moves from the first position 151 to a second position 152 while thethird object table W3T remains substantially on the exposure area 200.

[0090] The next stage during swap is depicted in FIG. 5 in which thesecond and third object tables are moved towards the second joint 105,155 of their respective conduit conducts 100, 150. In this position thesecond and third object tables are substantially between the exposurearea 200 and measuring area 300.

[0091] Finally, as is shown in FIG. 6, for exposure of the wafer held onthe second object table W2T, the second joint 105 of the first conduitconduct 100 is located at the first position 101 of the first conduitconduct 100. For measuring of the wafer on the third object table W3T,the second joint 155 of the second conduit conduct 150 is positioned atthe second position 152 rather than the first position 151.

[0092] The joints 105, 115, 155, 165 of the conduit conducts 100, 150have an angular range of motion of less than about 100° and in certainembodiments less than about 90°. This can be arranged by the correctpositioning of the first 101, 151 and second 102, 152 positions and thesizes of the exposure and measuring areas 200, 300. Furthermore, byallowing translation of the second joint 105, 155, the size of theconduit conducts and the exposure and measurement areas can beminimized.

[0093] The second and third object tables may be rotatable relative tothe second arm portion of their respective conduit conducts. Any numberof arm portions, rotational joint and translatable joints may make up aconduit conduct. The precise arrangement will depend on the requirementsand the number of degrees of freedom of the components with which theyare associated. In the following embodiments variations are described aswell as specific examples of the various components which make up theconduit conducts. It will be apparent to the skilled person that othervariations not described here are also possible.

[0094] Embodiment 2

[0095]FIG. 7 shows a conduit conduct 100 according to a secondembodiment which maybe is the same as the first embodiment save asdescribed below. In the second embodiment the second and third objecttables W2T, W3T are rotatably mounted to a main rotating joint 103. Inorder to perform swap, the main rotating joint 103 is rotated by 180°such that first and second object tables W2T, W3T swap positionsillustrated in FIG. 7. Positioning in the exposure and measurement areasis accomplished through rotation of positioning joints 125, 175 torotate the object tables W2T, W3T relative to main rotating joint 103and through extension and retraction of translating arm portion 107, 157out of and into receiving arm portion 109, 159. As in the firstembodiment, the moving surfaces of the translating arm portions may besealed using differential vacuum seals and air bearing assemblies 108,158.

[0096] Embodiment 3

[0097]FIG. 8 shows a conduit conduct 100 according to a third embodimentwhich may be the same as the first embodiment save as described below.FIG. 8 only shows a single conduit conduct 100 and object table W2T.This embodiment of a conduit conduct can equally well be applied to thecase where a third object table W3T is present and swap between themeasurement area 300 and the exposure area 200 is necessary. In thethird embodiment, the conduit conduct 100 has no rotational joints. Formaneuverability the conduit conduct 100 is provided with twotranslatable joints allowing extension/retraction in substantiallyorthogonal directions. The conduit conduct 100 is the same as that inthe first embodiment except that rotational first joint 115 is replacedby a translatable joint 118 and rotational second joint 105 is replacedby a fixed portion joining translating arm portion 107 at 90° to firstarm portion 110. Translatable joint 118 is of the same structure as thetranslatable joint in the first embodiment and is sealed with adifferential vacuum seal and air, or gas, bearing assembly 118.

[0098] Embodiment 4

[0099]FIG. 9 shows a conduit conduct 100 according to a fourthembodiment which maybe the same as the first embodiment save asdescribed below. In this embodiment the object table W2T is attached tothe end of translating arm portion 107. Receiving arm portion 109protrudes from a translatable plate 122 which is translatable (in adirection substantially orthogonal to the direction in which translatingarm portion 107 is translatable) relative to the vacuum chamber sidewall 21. Translatable plate 122 slides relative to vacuum side wall 21on an air bearing and differential vacuum seal arrangement 121.

[0100] Embodiment 5

[0101]FIG. 10a shows in detail a joint 115 of the conduit conduct 100 ofthe fifth embodiment. Other bearing types are also possible and thisdescription is given only as an example. In the schematic illustration,the joint 115 forms the hinge between the first arm portion 110 and thesecond arm portion 120. The joint may alternatively form the hingingmechanism between an arm portion 110, 120 and the vacuum chamber wall 21or an object table W2T, W3T. A passageway through the joint 115, thefirst arm portion 110, and second arm portion 120 allows conduits 24 topass through the conduit conduct 100. The joint 115 comprises a firstmember 26 with a cylindrical outer surface and a second member 28 with acylindrical inner surface. The second member 28 co-operates with thefirst member 26 and is rotatable co-axially with and relative to thefirst member 26. An air bearing 20 and differential vacuum seal 22 isprovided between opposing surfaces of first and second members 26, 28.

[0102] An alternative arrangement is shown in FIG. 10b in which thefirst and second members 26, 28 have flanges 27, 29 attached at theirends. The surfaces of the flanges oppose each other and an air bearing20 and vacuum differential seal 22 are provided between the opposingsurfaces.

[0103] The first and second members 26, 28 are formed as hollow openended pipes such that conduits 24 may pass through the centre of themembers. The first and second members 26, 28 are connected to the firstand second arm portions 110, 120 such that conduits can pass from thefirst arm portion 110 through the joint 115 and into the second armportion 120 with the only joining surfaces between the two arm portionsbeing sealed by a vacuum differential seal. This allows for freerotation of arm portions 110 and 120 relative to each other whileensuring that the conduits 24 inside the conduit conducts 100 are notexposed to the vacuum. Differential vacuum seals comprise at least onepassage exposed to a low pressure source. Optionally, a differentialvacuum seal can comprise several passages each exposed to successivelylower pressure sources. A differential vacuum seal is described in theseventh embodiment.

[0104] Embodiment 6

[0105]FIGS. 11 and 12 show a joint 115 according to a sixth embodimentof the invention which is the same as the first embodiment save asdescribed below. Joint 115 is provided such that first and second armportions 110, 120 are substantially in the same plane. The joint mayalternatively form the hinging mechanism between an arm portion 110, 120and the vacuum chamber wall 21 or an object table W2T, W3T. In thisembodiment, an inner member 32 with an at least partially cylindricalouter surface is provided at an end of a first hollow arm portion 110.As can be seen from FIG. 12, a second arm portion 120 is provided withan outer member 38 which has an at least partially cylindrical innersurface which co-operates with the outer surface of said inner member32. The inner surface of the inner member 32 has a first opening 34leading into said first arm portion 110 through which conduits 24 passand the inner surface of the outer member 38 has a second opening 40through which conduits 24 can pass into said second arm portion 120. Anair bearing 20 and differential vacuum seal 22 are provided aroundopenings 34 and 40 in between opposing surfaces of members 32 and 28.The inner member 32 is closed at the top and bottom of the cylindricalsurface such that the inside of the cylinder is not exposed to thevacuum. The sizes of the first and second openings 34, 40 in the innermember are dimensioned such that at any angle of desired rotation thefirst opening 34 and second opening 40 align such that conduits 24 canpass through said first arm portion 110 into said second arm portion120. Because this configuration allows first and second arm portions110, 120 to be in substantially the same (horizontal) plane, theconduits 24 are only bent and not twisted relative to each other as thearm portions 110, 120 rotate about the joint 115. This is advantageousbecause the lifetime of the conduits 24 can be increased by reducingtwisting and/or rubbing together.

[0106] Embodiment 7

[0107] An example of a gas bearing (“air bearing”) and differentialvacuum seal which can be used in the embodiments described above willnow be described referring to FIG. 13. FIG. 13 is a cross-sectionthrough a differential gas-bearing 108, showing part of a supportingmember, e.g. receiving translatable arm portion 109, and a supportedmember, e.g. translating arm portion 107. Gas bearing 108 holds thetranslating arm portion 107 off the receiving arm portion by a constantgap, g, of 5 μm, for example. For such a gap, the surface 109 b of thereceiving arm portion 109 in the vicinity of the bearing, and thesurface 107 b of the translating arm portion 107 over the area of travelof the bearing, must be finished to an RMS surface roughness of lessthan 0.8 μm, though they need not be flatter than 0.4 μm RMS surfaceroughness. This can readily be achieved with known mechanical polishingtechniques. In some applications a gap in the range of from 5 μm to 10μm may be appropriate and the surfaces need not be finished to such hightolerances. Clean air (or other gas, e.g. N₂) is supplied continuallythrough gas feed 211 at a pressure of several atmospheres to generate ahigh pressure region 214. The supplied air will flow towards acompartment M and also the vacuum chamber 20, where its presence would,of course, be undesirable. An escape path to atmospheric pressure isprovided via groove 212. To prevent further the air that forms the airbearing becoming an unacceptable leak into the vacuum chamber 20, it ispumped away via vacuum conduit 213. If desired, the escape path 212 mayalso be pumped. In this way, the residual leakage, 1, into the vacuumchamber 20 can be kept within acceptable levels.

[0108] Embodiment 8

[0109] An eighth embodiment of the invention is shown schematically inFIG. 14. This embodiment may be the same as the first embodiment save asdescribed below. Although only one conduit conduct and object table areshown, the same arrangement can be used for both second and third objecttables with respective first and second conduit conducts of the presentinvention as well as the first object table. Like references are usedwhere possible.

[0110] In the eighth embodiment, the object tables are connected topositioning means which are independent of the conduit conduct. Theconduit conduct may or may not include, for example, torque motors inthe second joint 105 and first joint 115. The second arm portion 120 ofthe conduit conduct is attached to the object table W2T with bellows 650through which conduits 24 pass. In this way, utilities are provided fromsecond joint 105 to object table W2T.

[0111] Object table W2T is connected to positioning means comprising afirst or long stroke module 620 and a second or short stroke module 630.Long stroke module 620 has a first range of motion relative to a frameof reference and short stroke module 630 is supported by the long strokemodule 620 and has a second range of motion, the second range of motionbeing smaller than the first range of motion.

[0112] The area over which long stroke module 620 can move is designatedBP. In this embodiment the area is provided with a planar motor magnetarray in base plate BP. Exposure area 200 and measuring area 300 in thisembodiment as shown in FIG. 3 also have a planar motor magnet array andareas outside of the exposure and measuring areas, especially betweenthe two areas, are also provided with a planar motor magnet array asnecessary.

[0113] The positioning means for the object table in the eighthembodiment of the present invention comprises planar motor coils 625 inthe long stroke module 620. Positioning of the short stroke module 630on the long stroke module 620 is accomplished by use of Lorentz-forcemotors 660 with 6 degrees of freedom. The planar motor and Lorentz-forcemotors are only schematically depicted in FIG. 14.

[0114] Embodiment 9

[0115] A ninth embodiment of the invention is shown schematically inFIG. 15. This embodiment may be the same as the first embodiment save asdescribed below. In FIG. 15, only a part of the second arm portion ofthe conduit conduct is illustrated. A tray 700 for coarse positioning ofthe object table is attached to the end of the second arm portion 120 ofthe conduit conduct which is positionable through use of planar motorcoils 705 and a planar motor magnetic array incorporated in base plateBP. Conduits are supplied to a first, long stroke module 620 of thepositioning means connected to object table W2T, through bellows 650.The positioning means for the long stroke module in this embodiment ofthe present invention comprises planar motor coils 625. As in the eighthembodiment a short stroke module 630, positioned on top of the longstroke module, is positioned by Lorentz-force motors 660 with 6 degreesof freedom.

[0116] Embodiment 10

[0117] A tenth embodiment of the present invention is illustratedschematically in FIG. 16. This embodiment may be the same as the firstembodiment save as described below. In this embodiment the position of atray 700 which carries the object table is determined by the conduitconduct whose first and second joints are driven by torque motors, forexample. The weight of the tray 700 is supported on surface BP by airbearings with differential vacuum seals 815. A bellows 830 and leafspring 835 arrangement in the arm portion 120 of the conduit conductnear the tray 700 allows a small amount of relative movement between theconduit conduct and the tray. Major positional movements are carried outby the torque motors in the conduit conduct joints but medium sizedmovements are carried out by movement of first module 620 and minormovements are carried out by movement of second module 630. First module620 is moved relative to tray 700 with the use of 6 degree of freedommedium stroke Lorentz-force actuators. Movement between the first module620 and the second module 630 is also accomplished using a 6 degrees offreedom Lorentz-force actuator. Gravity compensators may be employedwith Lorentz-force actuators to supply a force counteracting gravity forrelieving the Lorentz-force motors from delivering such a force.

[0118] The invention is described above in relation to variousembodiments; however it will be appreciated that the invention is notlimited by the above description. In particular, the invention has beendescribed above in relation to the wafer stage of a lithographicapparatus that is accommodated in a vacuum chamber. However, it willreadily be appreciated that the present invention is equally applicableto mask tables.

[0119] Further, the swap mechanisms disclosed may also be employed in anon-vacuum environment where utilities are provided to the object tablessuch that those utilities need not be disconnected during swap. A vacuumseal and conventional rolling bearings may be provided at places where adifferential vacuum seal and air or gas bearing are applied in theapplication. The construction of a vacuum seal and a conventional rollerbearing is less complex as the differential seal and the airbearingconstruction because no air/gas supply evacuation is needed in thejoints.

1. An assembly arranged to communicate at least one utility to a component located in a vacuum chamber, comprising a conduit constructed to communicate said at least one utility to said component, said component being moveable in said vacuum chamber, a conduit shield substantially enclosing a space comprising the at least one conduit and substantially separating said space from said vacuum chamber, said conduit shield being constructed and arranged to allow for movement of the component, wherein a vacuum generator is provided that is coupled to said space and which is constructed and arranged to provide a vacuum in said space comprising the at least one conduit. 